Multi-Carrier Transmitter Back-Off Estimation

1. A method in a wireless communication transmitter configured to transmit a multi-carrier signal, the multi-carrier signal being an aggregation of two or more separately modulated carriers occupying distinct frequency regions, comprising: obtaining, for each of the two or more carriers, a carrier-specific metric indicative of an amount by which the maximum transmit power on that carrier should be reduced from a pre-determined nominal maximum transmit power, if transmitted alone, to achieve a pre-determined out-of-band emission requirement; and estimating, by the wireless communication transmitter, a multi-carrier transmitter back-off metric for reducing the multi-carrier signal's maximum transmit power, based on the two or more carrier-specific metrics obtained.

2. The method of claim 1 wherein obtaining a carrier-specific metric comprises calculating the carrier-specific metric, or retrieving it from a lookup table, based on one or more configuration parameters of a signal on that carrier.

3. The method of claim 2 wherein the one or more configuration parameters comprise gain factors for the physical channels in a Wideband Code-Division Multiple Access (WCDMA) signal, or resource block allocations and modulation scheme in a Long Term Evolution (LTE) signal.

4. The method of claim 1 wherein obtaining a carrier-specific metric comprises obtaining a cubic metric, a peak-to-average power ratio, or a maximum-power reduction value.

5. The method of claim 1 wherein estimating the multi-carrier transmitter back-off metric is further based on a power ratio between the power of one or more channels on one of the carriers and the power of a corresponding one or more channels on other carriers.

6. The method of claim 5 wherein the power ratio comprises: a ratio between the power of all channels on one of the carriers and the power of all channels on other carriers; or a ratio between the power of a single control channel on one of the carriers and the power of a corresponding control channel on other carriers.

7. The method of claim 1 wherein estimating the multi-carrier transmitter back-off metric is further based on one or more configuration parameters of a signal on at least one of the carriers.

8. The method of claim 7 wherein the one or more configuration parameters comprise gain factors for the physical channels in a Wideband Code-Division Multiple Access (WCDMA) signal, or resource block allocations and modulation scheme in a Long Term Evolution (LTE) signal.

9. The method of claim 1 wherein estimating the multi-carrier transmitter back-off metric is based on a weighted sum of the two or more carrier-specific metrics obtained.

10. The method of claim 9 wherein the weight applied to each carrier-specific metric is a constant or, alternatively, depends on at least one of: a power ratio between the power of one or more channels on one of the carriers and the power of a corresponding one or more channels on other carriers; or one or more configuration parameters of a signal on at least one of the carriers.

11. The method of claim 9 wherein the weight applied to each carrier-specific metric depends on a power ratio between the power of one or more channels on one of the carriers and the power of a corresponding one or more channels on other carriers, and wherein the method further comprises calculating the weights, or retrieving them from a lookup table, based on the value of the power ratio or, alternatively, based on which one of a plurality of ranges the power ratio falls within.

12. A wireless communication transmitter configured to transmit a multi-carrier signal, the multi-carrier signal being an aggregation of two or more separately modulated carriers occupying distinct frequency regions, comprising: a multi-carrier transmitter back-off metric estimation circuit configured to: obtain, for each of the two or more carriers, a carrier-specific metric indicative of the amount by which the maximum transmit power on that carrier should be reduced from a pre-determined nominal maximum transmit power, if transmitted alone, to achieve a pre-determined out-of-band emission requirement; and estimate a multi-carrier transmitter back-off metric for reducing the multi-carrier signal's maximum transmit power, based on the two or more carrier-specific metrics obtained.

13. The wireless communication transmitter of claim 12 wherein the multi-carrier transmitter back-off metric estimation circuit is configured to obtain a carrier-specific metric by calculating the carrier-specific metric, or retrieving it from a lookup table, based on one or more configuration parameters of a signal on that carrier.

14. The wireless communication transmitter of claim 13 wherein the one or more configuration parameters comprise gain factors for the physical channels in a Wideband Code-Division Multiple Access (WCDMA) signal, or resource block allocations and modulation scheme in a Long Term Evolution (LTE) signal.

15. The wireless communication transmitter of claim 12 wherein the multi-carrier transmitter back-off metric estimation circuit is configured to obtain a carrier-specific metric as a cubic metric, a peak-to-average power ratio, or a maximum-power reduction value.

16. The wireless communication transmitter of claim 12 wherein the multi-carrier transmitter back-off metric estimation circuit is configured to estimate the multi-carrier transmitter back-off metric further based on a power ratio between the power of one or more channels on one of the carriers and the power of a corresponding one or more channels on other carriers.

17. The wireless communication transmitter of claim 16 wherein the power ratio comprises: a ratio between the power of all channels on one of the carriers and the power of all channels on other carriers; or a ratio between the power of a single control channel on one of the carriers and the power of a corresponding control channel on other carriers.

18. The wireless communication transmitter of claim 12 wherein the multi-carrier transmitter back-off metric estimation circuit is configured to estimate the multi-carrier transmitter back-off metric further based on one or more configuration parameters of a signal on at least one of the carriers.

19. The wireless communication transmitter of claim 18 wherein the one or more configuration parameters comprise gain factors for the physical channels in a Wideband Code-Division Multiple Access (WCDMA) signal, or resource block allocations and modulation scheme in a Long Term Evolution (LTE) signal.

20. The wireless communication transmitter of claim 12 wherein the multi-carrier transmitter back-off metric estimation circuit is configured to base the multi-carrier transmitter back-off metric on a weighted sum of the two or more carrier-specific metrics obtained.

21. The wireless communication transmitter of claim 20 wherein the weight applied to each carrier-specific metric is a constant or, alternatively, depends on at least one of: a power ratio between the power of one or more channels on one of the carriers and the power of a corresponding one or more channels on other carriers; or one or more configuration parameters of a signal on at least one of the carriers.

22. The wireless communication transmitter of claim 20 wherein the weight applied to each carrier-specific metric depends on a power ratio between the power of one or more channels on one of the carriers and the power of a corresponding one or more channels on other carriers, and wherein the multi-carrier transmitter back-off metric estimation circuit is further configured to calculate the weights, or retrieving them from a lookup table, based on the value of the power ratio or, alternatively, based on which one of a plurality of ranges the power ratio falls within.